1. Field of the Invention
This invention relates to a method and apparatus for producing thermal slide transparencies, and more particularly, to such a method and apparatus which is particularly suitable for producing color slide transparencies.
2. Description of the Prior Art
In one type of thermal printer, a dye-donor element is placed over a dye-receiving element, and the superposed elements are supported for cooperation with a print head having a plurality of individual heating resistors. When a particular heating resistor is energized, it causes dye from the donor to transfer to the receiver. The density or darkness of the printed color dye is a function of the energy delivered from the heating element to the donor. One of the problems in printers of this type is that the thermal time constant of the resistors is quite long. As a result, the printing speed is relatively slow, and the image contrast is limited.
It is known in thermal printing to use lasers instead of resistors to effect the transfer of dye from a donor element to a receiver element. In U.S. Pat. No. 4,804,975, for example, there is shown thermal dye transfer apparatus which comprises an array of diode lasers which can be selectively actuated to direct radiation onto a dye-carrying donor. Radiation from the diode lasers is modulated in accordance with an information signal to form an image on a thermal print medium. The diode laser array extends the full width of the print medium. A donor element in the form of a web is supported in contact with a receiver element which is mounted on a rotatable drum for movement with the web. When such apparatus is used for making a color image, the donor web must include separate spaced sections, for example, cyan, magenta, and yellow sections, and these sections must successively contact the receiver in separate passes of the drum. One problem in using the continuous web for a donor element is that the supply and take-up rolls make the apparatus rather large and bulky. A further problem is that use of the continuous-web donor limits the flexibility of the apparatus in that it is normally possible to only produce one kind of image, for example, a color image or a black-and-white image.